Thermoplastic polyester resins are conventionally and widely used as an engineering resin due to the well-balanced mechanical and physical properties that such resins exhibit. For example, polyester resins have been used as a material to form parts of precision instruments and electronic and electric components. The incorporation of an antistatic agent in such parts is usually indispensable so as to prevent dust accumulation which might deleteriously affect the part's performance characteristics and/or reliability.
Antistatic agents that have conventionally been used for thermoplastic polyester resins include sulfonate-type anionic antistatic agents, particularly metal alkylsulfonates and metal alkyl-aromatic sulfonates.
However, thermoplastic polyester resins containing such conventional sulfonate-type anionic antistatic agents are problematic in that they tend to decompose during extrusion or molding operations and thereby impair the melt stability of the resins to an extent that the resins are discolored and/or their properties decrease. Furthermore, the presence of such conventional anti-static agents can cause the polyester resins to "bubble" during kneading and extrusion so as to reduce the resins' bulk density. Thus, when strands of the resins are cooled with water during pelletizing, the water tends to be adsorbed into the bubbles and thereby prolong the drying time that is required. Thus, productivity is reduced.
One object of the present invention is to provide a thermoplastic polyester resin composition having thermal decomposition resistance and excellent antistatic properties. Broadly, therefore, the present invention is directed to an anti-static polyester resin which includes a combination of a sulfonate-type anionic antistatic agent and an organophosphorus compound, and/or an organic chelating agent.